The present invention relates to a playback speed control system for a reproducing apparatus which is applicable to control a playback speed of a VTR, for example.
It has been known in a conventional VTR that a playback speed is controlled in accordance with a rotational speed of a dial which is called a jog dial.
FIG. 1 shows an example of a playback speed control system for a conventional VTR. In FIG. 1, reference numeral 1 is a jog dial. Reference numeral 2 is a frequency generator mounted on a rotational axis of dial 1. In a conventional way, frequency generator 2 optically or magnetically generates pulses (FG pulses) P FG whose frequency corresponds to a rotational speed of dial 1.
Pulses P FG generated by frequency generator 2 are supplied to a counter 3 and are counted thereby in a certain period. Count data D PC obtained from counter 3 is supplied to an arithmetic processing unit 4 and is averaged by integration calculation thereby.
When a man rotates dial 1 in order to keep a constant playback speed, fluctuation of the rotational speed of dial 1 cannot be avoided. Therefore, FG pulses P FG having the corresponding fluctuation are generated by frequency generator 2. Because counter 3 counts FG pulses P FG in a certain period to make count data D PC, the rotation fluctuation of dial 1 results in the fluctuation of count data D PC. For this reason, arithmetic processing unit 4 averages the count data D PC by integration calculation so that the fluctuation of count data D PC is eliminated.
Count data D PCA averaged by arithmetic processing unit 4 is supplied to a tape transport speed command unit 5. Tape transport speed command unit 5 converts count data D PCA to a rotational speed of dial 1 and further converts it to a tape transport speed corresponding to the obtained rotational speed. To obtain the tape transport speed corresponding to the rotational speed, a table as shown in FIG. 2 is used, showing a relationship between a rotational speed of dial 1 and a tape transport speed. The table is stored, for example, in a ROM. FIG. 2 shows a relationship between a rotational speed of dial 1 in one direction and a tape transport speed. Although not shown in FIG. 2, when dial 1 is rotated in the other direction, a tape transport speed has a minus value.
Tape transport speed command unit 5 generates a command C SP to indicate a tape transport speed calculated in the above way. Command C SP is supplied to a tape transport system 6 so that a tape transport speed is controlled to be a speed indicated by command C SP.
FIG. 3 shows a flow-chart of processes of primary elements of the conventional apparatus as shown in FIG. 1. In FIG. 3, FG pulse P FG are counted in step S11, the count is integrated in step S12, command C SP is generated in step S13 based on the integral value and the tape speed control curve as shown in FIG. 2, and command C SP is supplied to tape transport system 6 in step S14.
According to an example as shown in FIG. 1, a table as shown in FIG. 2 is used such that when a rotational speed of dial 1 varies from 0 to 3 rotations per second, a tape transport speed simply varies from 0 to 3 times a normal speed. Because of the use of this table, a user needs to rotate dial 1 at a constant rotational speed in order to keep the constant tape transport speed in a range of 0 to 3 times a normal speed. It is very hard for the user to rotate dial 1 at a constant speed.
As explained above, in a conventional apparatus for controlling tape transport speed according to a rotational speed of dial 1, dial pulses (FG pulses PFG) may be averaged by some integral calculation. Tape transport system 6 is controlled according to command C SP based on the averaged pulse data (averaged count data D PCA).
However, when tape transport system 6 is controlled according to the averaged pulse data, a response of the tape transport speed control to the rotational speed of dial 1 is delayed due to the averaging process over the whole range of tape transport speeds to be controlled. Accordingly, an ease of use of the apparatus would be made worse.
On the other hand, if dial pulses (FG pulses P FG) are directly used without the integral calculation, fluctuation of the rotation of dial 1 would result in fluctuation of the tape speed.